JP2001019555A - Silicon nitride sintered compact and substrate using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a sintered compact having high thermal conductivity by making the sintered compact include a silicon nitride particle having a specific ppm or lower than it of the total content of oxygen, Al, Ca and Fe and a specific value or larger than it of a minor axis diameter orientated in one direction. SOLUTION: This silicon nitride sintered compact contains preferably 20-60 area % based on the whole silicon nitride sintered compact of a silicon nitride particle having <=1,000 ppm total content of oxygen, Al, Ca and Fe and >=2 μm minor axis diameter orientated in one direction. The ratio I (002)/I (200) of X-ray diffraction intensity I (200) of plane (002) of silicon nitride observed in the orientation direction to the X-ray diffraction intensity I (200) of plane (200) of silicon nitride is preferably >=40. Silicon nitride powder comprising 2-30 wt.% of a silicon nitride particle having >=2.5 average aspect ratio, containing <=300 ppm of Al and <=1 wt.% of oxygen and having >=30% β ratio is mixed with one or more of yttrium and/or a rare earth element and its compound and sintered to give the objective silicon nitride sintered compact.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride sintered body having excellent mechanical properties and high thermal conductivity, and moreover, a highly reliable nitride used for automobiles, vehicles, equipment and the like. The present invention relates to a silicon circuit board.

[0002]

2. Description of the Related Art Conventionally, alumina (Al) has been used as a circuit board for mounting a semiconductor element or the like which generates a large amount of heat.
_2. Description of the Related Art Circuit boards in which a conductive circuit layer is bonded to the surface of a ceramic substrate having excellent insulating properties, such as ₂ O ₃ ) ceramics, are widely used. However, in recent years, these semiconductor elements tend to increase in heat generation density with miniaturization and high performance of equipment, and in order to obtain reliable and stable operation, heat generated by the semiconductor element is dissipated. It has become an even more important issue to be able to sufficiently lower the temperature at which the junction of the element is not destroyed, and in addition to high electrical insulation properties as the characteristics of the circuit board, higher thermal conductivity is required. Is coming.

[0003] Substrate materials developed in response to these requirements include beryllia (BeO), silicon carbide (SiC),
Aluminum nitride (AlN) and the like, and those having a thermal conductivity exceeding 160 W / mK have been obtained.
However, BeO has high thermal conductivity and excellent heat dissipation, but has high toxicity and has a problem from the viewpoint of human body and environment. In addition, SiC and AlN also have high thermal conductivity and excellent heat dissipation properties, but have insufficient mechanical properties, and when used as a circuit board, require repeated thermal cycling or operating environment associated with the operation of a semiconductor element. There is a problem that cracks are likely to occur in the ceramic portion near the joint of the metal circuit layer due to the temperature change, and the reliability is low.

[0004] Silicon nitride (Si ₃ N ₄ ) is chemically stable at room temperature or high temperature and has excellent mechanical properties, and is therefore used as a structural material for automobile engine members and sliding members. In addition, recently, it has been used as a material for some circuit boards because of its high electrical insulation. However, since conventional Si ₃ N ₄ has lower thermal conductivity than AlN or the like, its use as an electronic material such as a circuit board is limited, and the range is considerably limited at present. It is.

Conventionally, Si ₃ N ₄ has been added to α-type silicon nitride powder,
Yttria (Y ₂ O ₃ ) or Al ₂ O ₃
After sintering aids are added and formed into a predetermined shape, the temperature is set to 2000 ° C. in a nitrogen pressurized atmosphere to prevent decomposition of silicon nitride.
In general, the sintered body is fired at a high temperature to obtain a densified sintered body, and is further formed by grinding into a desired shape.
However, sintering aids and SiO ₂ contained in raw silicon nitride powder
And Al ₂ O ₃ dissolve in the sintered silicon nitride grains or segregate at the grain boundaries, thereby scattering phonon, which is the main heat transfer medium in the ceramics, and failing to sufficiently increase the thermal conductivity.
It was about 0 W / mK, and its use was limited.

[0006] To solve these problems, Japanese Patent Laid-Open No. 4-219 has been proposed.
No. 371 discloses a method of obtaining Si ₃ N ₄ of 40 W / mK or more by reducing the content of Al and oxygen in a sintered body. Japanese Patent Application Laid-Open No. 6-135771 discloses a method for obtaining a sintered body of 60 W / mK or more by defining the amount of impurities in the sintered body and the amount of an auxiliary agent. Further, Japanese Patent Application Laid-Open No. Hei 165-265 discloses that a silicon nitride crystal of a sintered body is oriented so as to be 100 to 150 W /
A method for producing a silicon nitride sintered body having a mK is disclosed.

However, these methods do not consider the relationship between the heat transfer path and the impurities, and it is not only difficult to obtain a sintered body having high thermal conductivity stably, but also to obtain 160 W / The high thermal conductivity exceeding mK could not be obtained, and the application was also limited.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above prior art, and has as its object to stably provide a silicon nitride sintered body having higher thermal conductivity than conventional ones. An object of the present invention is to provide, for example, a semiconductor circuit board material for a power device by applying a sintered body.

[0009]

In order to achieve the above object, the present inventor has set forth the powder characteristics of silicon nitride powder, a molding method,
As a result of intensive studies on the sintering conditions, etc., it was found that by controlling the purity of the coarse particles of the silicon nitride sintered body and controlling the orientation of the coarse particles in consideration of the heat transfer path, heat conduction in any one direction was possible. The present inventors have found that a silicon nitride sintered body having greatly improved properties can be obtained, and have reached the present invention.

That is, as a result of an experimental study by the present inventors,
The sintered body of silicon nitride is better as the content of impurities is smaller, but particularly when oxygen, Al, Ca and Fe remain in the silicon nitride particles, phonon propagation in the silicon nitride particles is hindered. It has been found that the thermal conductivity of the silicon nitride sintered body decreases. And silicon nitride particles having a thermal conductivity of 130 W / mK or more easily when the total content of oxygen, Al, Ca, and Fe in the silicon nitride particles of a specific size is small and 1000 ppm or less. The present inventors have found that a sintered body can be obtained, and that when the silicon nitride particles are oriented in one direction, a thermal conductivity of 160 W / mK or more can be easily achieved in that direction, and the present invention has been achieved. Things.

As described above, in the silicon nitride sintered body of the present invention, specific impurities are limited to a specific amount in its microstructure.
Moreover, since silicon nitride particles developed to a specific size or more are present and the direction of the particles is oriented in any one direction, phonon propagation in that direction does not stop, and a high heat of 160 W / mK or more. Conductivity has been achieved. That is, the present invention contains silicon nitride particles having a total content of oxygen, Al, Ca, and Fe of 1000 ppm or less, and a minor axis diameter of 2 μm or more, and the minor axis diameter is 2 μm or more. A silicon nitride sintered body characterized in that silicon nitride particles are oriented in one direction.

Further, regarding the degree of the orientation, the X-ray diffraction intensity I (002) of the (002) plane of silicon nitride and the X-ray diffraction intensity I ( 200), the ratio I (002) / I (200)
The larger the value, the more preferable it is.

In the present invention, the amount of silicon nitride particles having a minor axis diameter of 2 μm or more preferably accounts for 20 to 60 area% of the entire silicon nitride sintered body from the viewpoint of achieving high thermal conductivity.

Since the silicon nitride sintered body of the present invention has the above characteristics, it has a characteristic of having a thermal conductivity of 160 W / mK or more in any one direction.

The method for obtaining the silicon nitride sintered body of the present invention can be easily obtained by the following method for manufacturing a silicon nitride sintered body of the present invention.

In the method for producing a silicon nitride sintered body of the present invention, a raw material powder obtained by adding at least one of yttrium and / or a rare earth element or a compound thereof as a sintering aid to a silicon nitride powder is sintered after molding. Belongs to the method of tying.

In the production method of the present invention, the silicon nitride powder used as a raw material is preferably as low as possible in impurities, but the oxygen, Al, and C in silicon nitride particles having a short axis diameter of 2 μm or more are obtained.
a, In order to make the total content of Fe 1000 ppm,
In particular, it is important to make Al 300 ppm or less and oxygen 1% by weight or less. Since Ca and Fe are discharged to the grain boundary phase in the process of growing and purifying silicon nitride particles generated during the sintering operation described later, 300 Ca is contained in the silicon nitride powder.
Tolerable to about 0 ppm.

When the β ratio of the silicon nitride powder is low, the purity of silicon nitride particles having a minor axis diameter of 2 μm or more in the obtained silicon nitride sintered body does not sufficiently increase, and high thermal conductivity is obtained. Therefore, it is necessary to be 30% or more. Even if a silicon nitride powder having a high α ratio and a silicon nitride powder having a high β ratio are sufficiently mixed and uniformly dispersed, a powder having a β ratio of 30% or more in X-ray diffraction may be used.

Further, the silicon nitride powder used as a raw material contains powder having an average aspect ratio of 2.5 or more by 2 to 30% by weight.
It is important to include When the average aspect ratio is smaller than 2.5, the degree of orientation of the obtained silicon nitride sintered body does not become sufficiently high. On the other hand, when it is too large, abnormal grain growth occurs vigorously during sintering, and A phenomenon in which the strength is extremely reduced may occur.

In the production method of the present invention, the molding method is not particularly limited, but the extrusion molding method has a high extrusion pressure and is a relatively advantageous method for causing orientation. It is important to add an organic binder to the raw material powder to form a green sheet in which silicon nitride particles in the silicon nitride powder are oriented. When increasing the thermal conductivity in the in-plane direction of the green sheet, it is used as it is as a molded body, and when increasing the thermal conductivity in the direction perpendicular to the surface of the green sheet, the oriented green sheet obtained above is used. A plurality of layers may be laminated and closely adhered to each other by a method such as pressing, and then cut in the laminating direction to form a molded body. After degreasing the above-mentioned molded body, by sintering, a silicon nitride sintered body having a high thermal conductivity of 160 W / mK or more in any one direction can be obtained. Furthermore, the silicon nitride sintered body of the present invention can also be manufactured by reducing the sheet thickness at the time of molding and increasing the number of laminated sheets by a pressing method, a doctor blade method, or the like.

As a sintering condition of the production method of the present invention, as a result, the total content of oxygen, Al, Ca, and Fe is 10%.
What is necessary is just to select so as to form silicon nitride particles having a minor axis diameter of 2 μm or more purified to 00 ppm or less. The specific sintering conditions are as follows.
° C / min, and the sintering temperature is 1800 ° C or more,
The product of sintering temperature and sintering time is 2 × 10 ⁴ ° C. · Hr to 2 × 1
And 0 ⁵ ℃ · Hr.

If the heating rate is lower than 0.5 ° C./min, abnormal grain growth is likely to occur, and if it is higher than 10 ° C./min, it is impossible to obtain sufficiently purified silicon nitride particles having a minor axis diameter of 2 μm or more. .

The sintering temperature needs to be 1800 ° C. or higher from the viewpoint of densification, but the present inventors have achieved the object of the present invention only when specific conditions are satisfied within this temperature range. The present invention has been made based on the finding that it can be achieved. That is, the product of the sintering temperature and the sintering time is 2 × 10 ⁴ ° C. · H
If it is less than r, the densification is not sufficient or the coarse grains are not sufficiently purified, and the thermal conductivity of the obtained silicon nitride sintered body is low. On the other hand, if the temperature is higher than 2 × 10 ⁵ ° C · Hr, the grain growth proceeds too much to lower the strength of the sintered body, and also the ratio of coarse particles becomes too large to secure a heat transfer path and lower the thermal conductivity. Also occurs.

The silicon nitride sintered body obtained by the present invention has an extremely high thermal conductivity as compared with the conventional one, and also has excellent electrical insulation and mechanical properties. It is suitable as a circuit board for an element having a large amount of generated heat to which a body cannot be applied, for example, a circuit board for a power module or the like.

In order to obtain the circuit board of the present invention, the above-mentioned silicon nitride sintered body is made into a plate shape, a metal plate such as copper or aluminum is laminated, and then a circuit is formed by a method such as etching or the circuit is formed. It can be achieved by a conventionally known method such as a method of joining metal plates.

The method of laminating the metal plate on the silicon nitride sintered body includes a method of joining using a brazing material, a method of directly joining the metal plate after providing an oxide layer on the silicon nitride sintered body, and a method of melting. Any method such as a method in which a metal is brought into contact with and bonded to a silicon nitride sintered body may be used.

[0027]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

Examples 1 to 10 and Comparative Examples 1 to 5 Using silicon nitride powders a to j having different characteristics shown in Table 1,
A sintering aid was added in Formulation C shown below, and thoroughly mixed with a Henschel mixer to obtain a raw material powder. To the obtained raw material powder, 18 parts by weight of a methylcellulose-based organic binder (“Selander” manufactured by Yuken Industries Co., Ltd.) was added and mixed, and then sufficiently stirred and mixed while gradually adding 12 parts by weight of water. Next, the obtained mixture was sufficiently kneaded while cooling with a kneader to form a compound, and the extrusion pressure was 180 k.
It was formed into a sheet by an extrusion method at g / cm ² . After cutting the obtained sheet into a shape that fits into a pressure-resistant container, laminating it, putting it in the stainless steel pressure-resistant container, and applying vacuum,
Pressure molding was performed at a pressure of 200 kg / cm ² from a direction perpendicular to the lamination surface. The obtained sheet or molded product is placed in a vacuum for 5 hours.
After degreased at 00 ° C., the degreased body was loaded into a container of boron nitride, sintered under the sintering conditions shown in Table 3 using an electric furnace of a carbon heater, and was sufficiently densified to a thickness of about 0.6 mm. A sintered body was obtained.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

With respect to the obtained sintered body, the following method is used.
An evaluation was performed. Table 4 shows the results. (1) Microstructure: The obtained various sintered bodies were subjected to surface roughening with a surface grinder and then mirror-polished with a lapping device.
Further, after etching with high-frequency plasma of 100 W in a gas atmosphere containing Ar-based oxygen and CF ₄ ,
The structure was observed by SEM. Next, quantitative evaluation of the area ratio of silicon nitride coarse particles having a minor axis diameter of 2 μm or more was performed by an image analyzer. (2) Orientation of silicon nitride particles: X-rays were applied from the direction in which the axis of the silicon nitride particles of the obtained sintered body was oriented, and X-ray diffraction was measured to obtain a silicon nitride (002) plane. Diffraction intensity I (002) and diffraction intensity I of silicon nitride (200) plane
The c-axis orientation was evaluated from the ratio of (200). Degree of orientation = [I (002) / I (200)] × 10
0 (3) β ratio: It was calculated by the following formula from the measurement result of the diffraction intensity of X-ray diffraction. β rate = ((Iβ ₁₀₁ + Iβ ₂₁₀ ) / (Iα ₁₀₂ + Iα ₂₁₀ +
_{Iβ 101 + Iβ 210)) ×} 100 (4) Thermal conductivity: to prepare a sample of .phi.10 × 3 mm was measured for thermal conductivity at room temperature using a Rigaku Corp. laser flash apparatus. (5) Oxygen content and impurity element content: The oxygen content of the sintered body and powder is pulverized with a mortar and pestle made of silicon nitride,
The analysis of metal-containing elements was quantitatively evaluated by an atomic absorption method using an O / N simultaneous analyzer of LECO. Further, the content of oxygen and the amount of metal element of the silicon nitride particles having a minor axis diameter of 2 μm or more can be determined by crushing the obtained sintered body with a mortar and pestle made of silicon nitride, and Journal of American Cera.
Mic Society Transactions July 1994, 185
After dissolving the grain boundary phase based on the method described on pages 7 to 1862, the silicon nitride particles having a minor axis diameter of less than 2 μm are removed by wet classification, and the metal content is quantitatively evaluated by the atomic absorption method. did.

[0033]

[Table 4]

Examples 11 to 15 Punched molded bodies were prepared in the same manner as in Example 2 by using the silicon nitride powder of Table 1c and adding sintering aids in formulations A to F shown in Table 2. . The obtained molded body was degreased at 500 ° C. in a vacuum, and then the degreased body was charged into a container of boron nitride, and sintered under an sintering condition 2 shown in Table 3 using an electric furnace of a carbon heater to obtain a sufficiently dense body. A sintered body having a thickness of about 0.6 mm was obtained. Evaluation of the obtained sintered body was performed in the same manner as in Example 1, and the results shown in Table 5 were obtained.

[0035]

[Table 5]

[Examples 16 to 20 and Comparative Examples 6-1]
0] Using a silicon nitride powder of Table 1c, a sintering aid was added in a formulation C shown in Table 2, and a punched compact was produced in the same manner as in Example 2. After degreased the obtained molded body at 500 ° C. in a vacuum, the degreased body was loaded into a container of boron nitride, and sintered under the sintering conditions 1 to 11 shown in Table 3 using an electric furnace of a carbon heater, A sufficiently densified sintered body having a thickness of about 0.6 mm was obtained. Evaluation of the obtained sintered body was performed in the same manner as in Example 1, and the results shown in Table 6 were obtained.

[0037]

[Table 6]

Example 21 A sheet obtained by the extrusion molding method in the same manner as in Example 2 using the silicon nitride powder of Table 1c and a sintering aid in the composition C shown in Table 2 was used. After lamination, it was placed in a stainless steel pressure-resistant container, evacuated, and pressure-formed at a temperature of 60 ° C. and a pressure of 200 kg / cm ² from a direction perpendicular to the lamination surface. The obtained molded body was cut out to a thickness of 0.8 mm so as to be perpendicular to the lamination surface to obtain a molded body. The obtained sheet was punched and formed into a predetermined size by a punching press machine. The obtained molded body was degreased in air at 500 ° C., and then subjected to Table 3 using a carbon heater electric furnace.
Under the sintering condition 2 shown in Table 2 to obtain a sintered body having a thickness of about 0.6 mm. Evaluation of the obtained sintered body was performed in the same manner as in Example 1, and the results shown in Table 7 were obtained.

[0039]

[Table 7]

Example 22 After laminating the sheets in the same manner as in Example 21, a load of 10 t was applied to the sheet by using a hydrostatic pressure press.
The resulting molded body was cut out to a thickness of 0.8 mm so as to be perpendicular to the lamination surface to obtain a molded body. The obtained sheet was punched and formed into a predetermined size by a punching press machine. The obtained molded body is in air at 500 ° C.
After degreased in, sintering was performed under the sintering conditions 2 shown in Table 3 using an electric furnace of a carbon heater to obtain a sintered body having a thickness of 0.6 mm. Evaluation of the obtained sintered body was performed in the same manner as in Example 1, and the results shown in Table 7 were obtained.

[Embodiments 23 and 24] The embodiment 23 and the embodiment 24 are manufactured in the same manner as in the embodiment 21 and then ground, and then sintered to a size of 40.times.60.times.0.6 mm. The body was used. The thermal conductivity of each sintered body was 172 W / mK in Example 23 in the plane direction, and 162 W / mK in Example 24 in the direction perpendicular to the plane.

Next, Ag-
Using a Cu-Ti-based brazing material, a 0.3 mm copper plate is laminated on the circuit side and a 0.15 mm copper plate is laminated on the other side.
Heat bonding at 835 ° C for 40 minutes in a vacuum of ^-2 Pa or less,
A composite was made. Next, a circuit pattern was printed with an etching resist, and after a curing treatment, a pattern was formed using an aqueous ferric chloride solution to produce a circuit board. These circuit boards were subjected to 1000 heat cycle tests at a temperature range of −40 ° C. to 125 ° C., and then visually inspected and inspected for abnormalities such as cracks and peeling of the copper plate by an ultrasonic flaw detector. , Was not recognized at all.

[Examples 25 and 26] In Examples 25 and 26, both surfaces of a silicon nitride sintered body of 40 × 60 × 0.6 mm obtained in the same manner as in Example 24 were obtained. A 0.4 mm aluminum plate is laminated using an Al-Si brazing material, and 600 mm in a vacuum of 10 ^-2 Pa or less.
Heat bonding was performed at 30 ° C. for 30 minutes to produce a composite. Next, a circuit pattern was printed with an etching resist, and after a curing treatment, a pattern was formed using an aqueous ferric chloride solution to produce a circuit board. These circuit boards are moved from -40 ° C to 12
After performing a heat cycle test 1000 times at a temperature range of 5 ° C., an appearance inspection and an ultrasonic flaw detector were used to check for any abnormality such as cracks or peeling of the copper plate, but none were found.

[0044]

According to the silicon nitride sintered body of the present invention, silicon nitride particles of a specific size in which a specific element is limited to a specific amount or less in a sintered body are oriented in one direction, and heat conduction in that direction is performed. Since it has the characteristic that the rate reaches 160 W / mK or more, as a circuit board material for a power device mounting a high heat-generating element or the like, which cannot be applied in a conventional silicon nitride sintered body, Alternatively, it can be used as a heat dissipating component or material in a wide range of fields such as electric railways, automobiles, and equipment.

The method for producing a silicon nitride sintered body of the present invention is industrially very useful because the silicon nitride sintered body can be easily produced with good reproducibility.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masahiro Ibukiyama 3-5-1 Asahimachi, Machida-shi, Tokyo Denki Kagaku Kogyo Co., Ltd. Central Research Laboratory F-term (reference) 4G001 BA08 BA09 BA12 BA14 BA32 BA71 BA73 BB08 BB09 BB12 BB14 BB32 BB71 BB73 BC12 BC14 BC22 BC52 BD03 BE12 BE22 BE31

Claims (10)

[Claims] 1. A silicon nitride particle having a total content of oxygen, Al, Ca and Fe of 1000 ppm or less and a minor axis diameter of 2 μm or more, and said minor axis diameter is 2 μm or less.
A silicon nitride sintered body characterized in that the silicon nitride particles are oriented in one direction. 2. The X-ray diffraction intensity I (002) of the (002) plane and the X-ray diffraction intensity I (200) of the silicon nitride in the direction in which silicon nitride particles having a minor axis diameter of 2 μm or more are oriented.
2. The silicon nitride sintered body according to claim 1, wherein a ratio I (002) / I (200) of (200) is 40 or more. 3. 3. The silicon nitride sintered body according to claim 1, wherein the silicon nitride particles having a minor axis diameter of 2 μm or more occupy 20 to 60% by area of the whole silicon nitride sintered body. Union. 4. The thermal conductivity in any one direction is 160 W / mK.
4. The silicon nitride sintered body according to claim 1, 2 or 3, wherein: 5. A method for producing a silicon nitride sintered body, comprising forming a raw material powder obtained by adding at least one compound of yttrium and / or a lanthanoid group element to a silicon nitride powder, followed by sintering. Containing 2 to 30% by weight of silicon nitride particles having a ratio of 2.5 or more;
Contains not more than 00 ppm and not more than 1% by weight of oxygen, and has a β ratio of 3
Using silicon nitride powder of 0% or more, firing while growing silicon nitride particles such that the total content of oxygen, Al, Ca, and Fe of the silicon nitride particles having a minor axis diameter of 2 μm or more is 1000 ppm or less. A method for producing a silicon nitride sintered body. 6. A green sheet formed by adding an organic binder to a raw material powder in a molding operation so that silicon nitride particles in the silicon nitride powder are oriented in one direction, and degreased. Item 6. The method for producing a silicon nitride sintered body according to Item 5. 7. In a molding operation, an organic binder is added to the raw material powder to obtain a green sheet molded so that the silicon nitride particles in the silicon nitride powder are oriented in one direction.
6. The method for producing a silicon nitride sintered body according to claim 5, wherein a plurality of the green sheets are cut in a laminating direction in a laminating direction to form a molded body and degreased. 8. The sintering operation is performed at a rate of 0.5 to 10 ° C./min after the rate of temperature rise exceeds at least 1500 ° C., the sintering temperature is 1800 ° C. or more, and the sintering temperature and The product of sintering time is 2 × 10 ⁴ ℃ ・ Hr ~ 2 × 10 ⁵ ℃ ・
8. The method for producing a silicon nitride sintered body according to claim 5, wherein the temperature is Hr. 9. A silicon nitride circuit substrate comprising the silicon nitride sintered body according to claim 1, 2, 3, or 4. 10. The silicon nitride circuit board according to claim 9, wherein the high thermal conductivity direction of the silicon nitride sintered body is oriented in a direction perpendicular to the circuit board.